Water purifying system

ABSTRACT

The invention relates to a system for water purification comprising at least two units, of which the first unit comprises at least one filter unit ( 1 ) which consists of a container ( 2 ) containing a filter bed ( 3 ) of zeolite, and of which the second unit ( 4 ) consists of a container ( 5 ) enclosing a UV lamp ( 6 ). The two units are connected to each other by means of a conduit ( 7 ) for conveying water. According to the invention, the filter bed ( 3 ) consists of at least 50% by weight natural zeolite with a pore diameter of 0.05-5 nm. The pressure in the filter bed is 1-4 bar and the UV lamp ( 6 ) has a light intensity of 300-500 J/m 2 .

The present invention relates to a system and a method of purifyingwater. More particularly, the invention relates to a system and a methodof purifying water of pathogenic micro-organisms such as Giardia andCryptosporidium.

Polluted drinking water is a great problem and causes mild affections aswell as serious diseases and even deaths. In the US, a number of seriousoutbreaks have been registered as a consequence of drinking water beingpolluted. Especially harmful effects are caused by the water-borneparasites Giardia and Cryptosporidium. A crucial problem with theseorganisms is that they cannot be efficiently eliminated from water byapplying known methods. The organisms can be found in the whole world,but are most common in warm countries and they cause diarrhoea, stomachpain and nausea. The most serious outbreak of cryptosporidiosis in theUS occurred in 1993 in Milwaukee in which 400,000 people were taken illwith polluted drinking water.

Normally, drinking water is purified in several steps such as byflocculation, sedimentation, filtration through sand and chlorination.However, micro-organisms have an incredible ability to adjust todifferent environments and they gradually become resistant to commonbactericidal systems and disinfectants. Cryptosporidium is, forinstance, resistant to chlorine and can resist 3% chlorine for 18 hours.However, the WHO recommend only 0.5 ppm chlorine in drinking water.

In U.S. Pat. No. 5,935,431, an integrated filtration and sterilisationapparatus is described. In the apparatus, inlet water is first filteredthrough a filter bed of, for instance, active carbon, adsorption resin,zeolite, reduction catalysts, paper, polymers, clay, metals, etc. Thefilter material in this apparatus serves to separate particulate,organic or inorganic compounds from inlet water. If an inorganicmaterial, such as heavy metals or sulphites, is to be removed, thefilter material is preferably an ion-exchange resin, a zeolite or areduction catalyst. The permeate, i.e. the filtered inlet water, is thenexposed to UV radiation and ozone treatment, said ozone treatment givingrise to bacterial killing.

Besides being resistant to chlorine, Cryptosporidium is also veryresistant to UV radiation and ozone. 1 ppm ozone for 5 minutes resultsin only 90% killing. However, such high concentrations of ozone are notpermitted; only 0.4 ppm is permitted in outlet water intended fordrinking water.

U.S. Pat. No. 5,935,431 does not mention how many ppm ozone are added tothe outlet water, but this method suffers from the drawback that inozone treatment degradation products form from the killed bacteria. Itis not advisable to directly use the water discharged from thisapparatus as drinking water, on the one hand, owing to the degradationproducts formed and, on the other, owing to possibly remaining ozone.

Both Giardia and Cryptosporidium have a spore stage in their lifecycles. The spores are much smaller than the actual organisms and theoocysts of Cryptosporidium can be as small as 4 μm. Today, onlyultrafiltration or reverse osmosis can separate such small particles,but the methods are too expensive to be used for large volumes of water.

Thus there is a great need for a new system for purifying drinking waterwhich is capable of dealing with Cryptosporidium, Giardia and otherpathogenic, water-borne micro-organisms.

One object of the present invention is to provide a system and a methodin which water containing Cryptosporidium and Giardia can be efficientlypurified with excellent results.

Other objects, features and advantages of the present invention will beapparent from the description below.

These objects are achieved by a system and a method according to theindependent claims. Particularly preferred embodiments are defined inthe dependent claims.

In short, the present invention relates to a system for waterpurification comprising at least two units, of which the first unitcomprises at least one filter unit which consists of a containercontaining a filter bed of zeolite, and of which the second unitconsists of a container enclosing a UV lamp. The two units are connectedto each other by means of a conduit for conveying water. According tothe invention, the filter bed consists of at least 50% by weight naturalzeolite with a pore diameter of 0.05-5 nm. The pressure in the filterbed is 1-4 bar and the UV lamp has a light intensity of 300-500 J/m².

It has, surprisingly, been found that excellent results are achievedwhen water containing Cryptosporidium and Giardia is purified inaccordance with the method and the purifying system according to thepresent invention. Preliminary results show that a substantiallycomplete reduction of Cryptosporidium and Giardia is obtained.

Preferred embodiments of the present invention will be described below,partly with reference to the accompanying drawing. The drawing must notbe considered to limit the scope of the present invention.

The FIGURE is a schematic view of the system according to a preferredembodiment of the present invention.

Water purifying systems according to the present invention comprises atleast two units. The first unit comprises at least one filter unit 1,which consists of a container 2 containing a filter bed 3 of zeolite.The second unit 4, the UV unit, consists of a container 5 enclosing a UVlamp 6. At the filter unit 1, the system is provided with an inlet 9 andat the UV unit 4 with an outlet 10. The two units are connected to eachother by means of conduits 7 for conveying water, and the water movesthrough the purifying system in the direction shown by the arrows P1.

The filter bed 3 consists of at least 50% by weight natural zeolite,which preferably is clinoptilolite and/or mordenite. The zeolite has apore diameter of 0.05-5 nm, preferably 0.08-3 nm and most preferably0.1-1 nm. The grain size of the zeolite is 0.1-2.5 mm, preferably0.6-2.0 mm.

The filter bed 3 has an inner filter surface of 50-600 m²/g, preferably200-500 m²/g, and during operation the pressure in the filter bed is 1-4bar, preferably 1.5-3.5 bar and most preferably 2.5-3.4 bar. Thepressure is important for the zeolite to be compacted in the filter bed3 and providing the desired purifying capacity. The pressure in thefilter bed should be so high that particles larger than 1 μm get caughtand stay in the filter. The pressure can be regulated by means of awater pump (not shown) for inlet water. A throttle valve 11 after thefilter unit 1 makes it possible to quickly raise the pressure in thefilter unit.

Besides the natural zeolite, the filter bed 3 can also containmontmorillonite, quartz, feldspar and vulcanised rock crystal.

The zeolite in the filter bed must have a certain hardness to be able toresist the pressure in the filter bed and should be able to resist apressure of at least 2.5 bar, preferably at least 4 bar, and also beable to resist pressure fluctuations of up to 6 bar.

If several filter units are used, they can be connected either inparallel or in series.

The UV radiation takes place at a wave length of 200-280 nm, preferably254 nm with a lamp 6 with a UV-C filter. The light intensity shouldpreferably be 300-500 J/m², more preferably 350-450 J/m² and mostpreferably 400-430 J/m². UV light with a normal light intensity of about250 J/m² does not provide the desired killing effect on themicro-organisms.

To ensure that the particle size is less than 1 μm at all points of timein the purification process, also after back flushing for cleaning thefilter unit, a bag filter 8 can be placed between the filter unit 1 andthe UV unit 4. The bag filter 8 is preferably made of polypropylenehaving a mesh size of less than 1 μm. As an alternative to the bagfilter 8, it is possible (in a manner which is not shown in the FIGURE),after back flushing for cleaning the filter unit 1, to let waterdischarged from the filter unit return to the inlet 9 in the filter unit1 until a sufficiently high pressure has been built up in the filter bed3.

The present invention also relates to a method of purifying water, inparticular of Cryptosporidium, in which the water is exposed to theabove-described purifying system, for producing drinking water.

Even if the advantages of the invention have been described withreference to drinking water, the purifying system can, of course, beused for purifying other types of water, of which swimming-pool water isof particular interest.

When affording aid to emergency areas and countries devastated by war,it is important to have reliable, rapid, simple and cheap systems athand for purifying water. One embodiment of the invention relates to amobile purifying system for use in the field, which involves theabove-described purifying system. In this case, the purifying system ismounted on a trailer and comprises a pump for pumping surface water, asludge filter, filter units with a filter bed of zeolite, possibly a bagfilter, a UV source, chlorinating equipment and a collection tank forthe purified water.

What is claimed is:
 1. A water purification system comprising at leasttwo units, of which the first unit comprises at least one filter unitwhich includes a container containing a filter bed of zeolite, and ofwhich the second unit includes a container enclosing a UV lamp, said twounits being connected to each other by a conduit for conveying water,the filter bed having at least 50% by weight natural zeolite with a porediameter of 0.05-5 nm, the pressure in the filter bed being 1-4 bar, andthe UV lamp having a light intensity of 300-500 J/m ², wherein a bagfilter is arranged between the filter unit and the UV unit to ensure aparticle size of less than 1 μm also after back flushing of the filterunit.
 2. The system as claimed in claim 1, wherein the natural zeolitein the filter bed includes one of clinoptilolite and/or mordenite. 3.The system as claimed in claim 1, wherein the filter bed has an innerfilter surface of 50-600 m²/g.
 4. The system as claimed in claim 1,wherein the filter bed has an inner filter surface of 200-500 m²/g. 5.The system as claimed in claim 1, wherein the zeolite has a porediameter of 0.08-3 nm.
 6. The system as claimed in claim 1, wherein thezeolite has a pore diameter of 0.1-1 nm.
 7. The system as claimed inclaim 1, wherein the light intensity of the UV lamp is 350-450 J/m². 8.The system as claimed in claim 1, wherein the light intensity of the UVlamp is 400-430 J/m².
 9. The system as claimed in claim 1, wherein thepressure in the filter unit is 1.5-3.5 bar.
 10. The system as claimed inclaim 1, wherein the pressure in the filter unit is 2.5-3.4 bar.
 11. Thesystem as claimed in claim 1, wherein the grain size of the zeolite is0.1-2.5 mm.
 12. The system as claimed in claim 1, wherein the grain sizeof the zeolite is 0.6-2.0 mm.
 13. The system as claimed in claim 1,wherein the zeolite in the filter bed is able to resist a pressure of atleast 2.5 bar.
 14. A method of filtering water to eliminateCryptosporidium, the method comprising: passing water through a filterunit containing a filter bed of zeolite consisting of at least 50%natural zeolite with a pore diameter of 0.05-5 nm and a grain size of0.1-2.5 mm, the pressure in the filter bed being 1-4 bar; and radiatingthe water with UV-light having a light intensity of 300-500 J/m².
 15. Awater purification system comprising at least a first unit including atleast one filter unit having a filter bed of zeolite, and a second unithaving a UV lamp, said first and second units being connected togetherby a conduit adapted to convey water, the filter bed having at least 50%by weight natural zeolite with a pore diameter of 0.05-5 nm and a grainsize of 0.1-2.5 mm, the pressure in the filter bed being 1-4 bar, andthe UV lamp having a light intensity of 300-500 J/m².
 16. The system asclaimed in claim 15, wherein the natural zeolite includes one ofclinoptilolite and/or mordenite.
 17. The system as claimed in claim 15,wherein the filter bed has an inner filter surface of 50-600 m²/g. 18.The system as claimed in claim 15, wherein the filter bed has an innerfilter surface of 200-500 m²/g.
 19. The system as claimed in claim 15,wherein the zeolite has a pore diameter of 0.08-3 nm.
 20. The system asclaimed in claim 15, wherein the zeolite has a pore diameter of 0.1-1nm.
 21. The system as claimed in claim 15, wherein the light intensityof the UV lamp is 350-450 J/m².
 22. The system as claimed in claim 15,wherein the light intensity of the UV lamp is 400-430 J/m².
 23. Thesystem as claimed in claim 15, wherein the pressure in the filter unitis 1.5-3.5 bar.
 24. The system as claimed in claim 15, wherein thepressure in the filter unit is 2.5-3.4 bar.
 25. The system as claimed inclaim 15, wherein the grain size of the zeolite is 0.6-2.0 mm.
 26. Thesystem as claimed in claim 15, wherein the zeolite in the filter bed isarranged to resist a pressure of at least 2.5 bar.